Think I need to give an honorable mention to a game from 1995 that I played a lot back in the day and still pick up from time to time.
My favorite scrolling shooter Tyrian.
Filled with secrets and a great generator system. Being able to collect money to buy and upgrade your weapon arsenal - something I miss in pretty much every other game in the genre. The graphics look a bit stale by todays standard, but the gameplay and music holds up well. It is released as freeware and a lot of community created ports exists to play it on different systems.